Stress monitoring of roadway supporting bolt based on fiber  bragg grating technology

The effect of bolt support determines the quality and efficiency of roadway support. In actual production,there has always been the problem of failure of the support caused by the collapse of the bolt,which has brought potential safety hazards to coal mine production. At present,bolt (cable) dynamometers and surface-mounted sensor are mainly used for bolt monitoring in China,but the dynamometers cannot monitor and analyze the service status of the bolts. Although surface-mounted sensors can measure the stress of the rods,its industrial application effect is poor. In this paper,a mine-used fiber Bragg grating bolt sensor technology was proposed to monitor the stress of the bolt body. The sensor takes the advantages of the small size and tensile strength of the grating,connects several Bragg gratings in chains and embeds them in the bolt so as to realize the analysis of the stress change law of the bolt body and the prediction and early warning function of the fracture of the bolt body. The system is tested by industrial experiment. 32 groups of anchor sensors are installed at a position of 200 meters in front of the working face,with a total of 160 data acquisition points. The self-developed 32 channel demodulation equipment is used to collect and store the grating data,and the data is analyzed and verified combined with the advancing speed of the working face. The results show that the influence range of the working face mining on the force of the bolt body is about 60 m,and the influence is weak when it is beyond 60 m,but after entering 50 m,the stress change of the bolt body increases significantly,and the deformation occurs at the two sides of the channel;The change of the bolt body in the inner side is more obvious than that in the outer side on the same section. The local stress change of the outer side rod body is about 30 kN,and the local stress change of the inner side rod body can reach 150 kN. The stress of a single bolt body presents a nonlinear change state,and the maximum position of the bolt stress changes with the advancement of the working face. The stress is mainly concentrated in the position where the bolt is close to the tray and buried deep in the roadway;The deformation of the anchor rod body receives the dual effects of axial tension and radial shear force;According to the analysis of single day stress of bolt,it is concluded that the rod body is not in the process of constant deformation,and the rod body enters a stable state after completing one deformation.until the next pressure or disturbance.